A field effect transistor (hereafter abbreviated as “FET”) is a semiconductor element which includes three terminals of a source electrode, a drain electrode and a gate electrode, wherein electric current flowing a channel connected to the source electrode and the drain electrode is controlled by electric field generated by a voltage impressed to the gate electrode. For example, carbon nanotube field effect transistor (hereafter abbreviated as “CNT-FET”), in which a channel across the source electrode and the drain electrode is composed of carbon nanotube (hereafter abbreviated as “CNT”), is known.
As one example of CNT-FET, those shown in FIG. 1A and FIG. 1B are known (e.g., Non-patent document 1).
In CNT-FET shown in FIG. 1A, source electrode 3 and drain electrode 4, as well as a channel for connecting these electrodes are disposed on insulating film 1 formed on a first plane of substrate 2, and gate electrode 5 electrically connected to silicone substrate 2 is disposed on a second plane. FET with such a configuration is referred to as a back-gate field effect transistor (hereafter abbreviated as “back-gate FET”).
With FET shown in FIG. 1B, source electrode 3, drain electrode 4, and gate electrode 5 are disposed on insulating film 1 formed on the first plane of substrate 2. FET of this sort is referred to as, based on arrangement of the gate electrode, side-gate field effect transistor (hereafter abbreviated as “side-gate FET”).
Further, developments of sensors utilizing electric characteristics of CNT-FET have been promoted extensively (e.g., Patent Document 1). These sensors utilize the fact that electric characteristics of CNT that serves as a channel change depending on change of state of a molecule recognizing part bound or immobilized to CNT. For example, reaction between the molecule recognizing part and a detection target substance is detected by a change in electric current between source electrode and drain electrode of CNT-FET (hereafter referred to as “source-drain current”) or in voltage (hereafter referred to as “source-drain voltage”) via changes in electric characteristics of CNT induced by the reaction.    Patent Document 1: WO2004/104568 pamphlet    Non-patent Document 1: K. Matsumoto, “Application of carbon nanotube SET/FET to sensors”, Brochure presented at electronic materials study committee, The Institute of Electrical Engineers of Japan, Vol. EFM-03, Nos. 35-45, Dec. 19, 2003, pp. 47-50